1. Technical Field
The present invention relates to an organic electroluminescent display (OELD) device, and more particularly, to an OELD device having a high aperture ratio and a high resolution.
2. Related Art
An OELD device of new flat panel display devices is a self-emitting type. The OELD device has excellent characteristics of a view angel, a contrast ratio and so on. Also, since the OELD device does not require a backlight assembly, the OELD device has low weight and low power consumption. Moreover, the OELD device has advantages of a high response rate, a low production cost and so on. In addition, all elements of the OELD device are a solid phase, the device is strong against an outer impact. Particularly, there is a big advantage in a production cost. A fabricating process of the OELD device is very simple and requires a deposition apparatus and an encapsulating apparatus. The OLED device may be called to as an organic light emitting diode device.
In an active matrix type OELD device, a voltage for controlling an electric current of a pixel is charged in a storage capacitor such that a level of the electric current is maintained to next frame.
FIG. 1 is a circuit diagram of one sub-pixel region of the related art OELD device. As shown in FIG. 1, an OELD device includes a gate line “GL”, a data line “DL”, a power supply line “PL”, a switching thin film transistor (TFT) “Ts”, a storage capacitor “Cst”, a driving TFT “Td”, and an emitting diode “Del”. The gate line “GL” and the data line “DL” cross each other to define a sub-pixel region “SP”. The switching TFT “Ts” is connected to the gate and data line “GL” and “DL”, the driving TFT “Td” and the storage capacitor “Cst” are connected to the switching TFT “Ts” and the power line “PL”. The emitting diode “Del” is connected to the driving TFT “Td”.
When the switching TFT “Ts” is turned on by a gate signal applied through the gate line “GL”, a data signal from the data line “DL” is applied to the gate electrode of the driving TFT “Td” and an electrode of the storage capacitor “Cst”. When the driving TFT “Td” is turned on by the data signal, an electric current is supplied to the emitting diode “Del” from the power line “PL”. As a result, the emitting diode “Del” emits light. In this case, when the driving TFT “Td” is turned on, a level of an electric current applied from the power supply line “PL” to the emitting diode “Del” is determined such that the emitting diode “Del” can produce a gray scale. The storage capacitor “Cst” serves to maintain the voltage of the gate electrode of the driving TFT “Td” when the switching TFT “Ts” is turned off. Accordingly, even if the switching TFT “Ts” is turned off, a level of an electric current applied from the power supply line “PL” to the emitting diode “Del” is maintained to next frame.
To produce full color images, the OELD device includes red, green and blue sub-pixel regions in one pixel region. FIG. 2 is a schematic view showing pixel regions of the related art OELD device. As shown in FIG. 2, the OELD device 10 includes a plurality of pixel regions “P”. Each pixel region “P” includes red, green and blue sub-pixel regions “SPr”, “SPg” and “SPb”.
Each pixel region “P” has a rectangular shape to have a horizontal length “H” and a vertical length “V”. The red, green and blue sub-pixel regions “SPr”, “SPg” and “SPb” are arranged in each pixel region “P” along a horizontal direction or a vertical direction. For example, each of the red, green and blue sub-pixel regions “SPr”, “SPg” and “SPb” has a horizontal length corresponding to ⅓ of the horizontal length “H” of the pixel region “P” and a vertical length corresponding to the vertical length “V” of the pixel region “P”.
Red, green and blue emitting layers 32, 34 and 36 are respectively formed in the red, green and blue sub-pixel regions “SPr”, “SPg” and “SPb”. The red, green and blue emitting layers 32, 34 and 36 constitute the emitting diode “Del” with first and second electrodes (not shown). When the emitting layers are closely disposed, a shadowing problem, i.e., a color mixture in adjacent sub-pixel regions, is generated. Accordingly, each of the emitting layers 32, 34 and 36 has a width “w”, i.e., a horizontal length, and a height “h”, i.e., a vertical length, and is spaced apart from each other by a first distance “d1”.
The red, green and blue emitting layers 32, 34 and 36 are formed by a thermal deposition using a shadow mask. In FIG. 2, the red, green and blue emitting layers 32, 34 and 36 are overlapped portions of the first and second electrodes.
An area of the red, green and blue emitting layers 32, 34 and 36 may be larger than that in FIG. 2. However, since an area of the red, green and blue emitting layers 32, 34 and 36 corresponding to the overlapped portions of the first and second electrodes is effective emitting portions, the red, green and blue emitting layers 32, 34 and 36 corresponding to the overlapped portions are shown.
The OELD device 10 display full color images using the red, green and blue emitting layers 32, 34 and 36 in the red, green and blue sub-pixel regions “SPr”, “SPg” and “SPb”.
Recently, to meet requirement for a high resolution, an area of one pixel region “P” and an area of each of the red, green and blue sub-pixel regions “SPr”, “SPg” and “SPb” are reduced.
As a result, an area for the red, green and blue emitting layers 32, 34 and 36 is also reduced. The height “h” of each of the red, green and blue emitting layers 32, 34 and 36 substantially corresponds to the vertical length “V” of the pixel region “P” such that there is no problem. However, since the width “w” of each of the red, green and blue emitting layers 32, 34 and 36 corresponds to the horizontal length “H” of the pixel region “P”, there is a limitation in reducing the width “w”.
Namely, the first distance “d1” between adjacent emitting layers for preventing the shadowing problem should be maintained when an area of the pixel region “P” is reduced because of the requirement of a high resolution.
Accordingly, with a high resolution of the OELD device, an area for the red, green and blue emitting layers 32, 34 and 36 is rapidly reduced such that it is difficult to fabricate a fine shadow mask for forming the red, green and blue emitting layers 32, 34 and 36.